For the band, see Pulley (band). For the village, see Pulley, Shropshire.
 Pulleys on a ship. In this context, pulleys are usually known as blocks.
A pulley (also called a sheave or block) is a wheel with a groove between two flanges around its circumference. The groove normally locates a rope, cable or belt. Pulleys are used to change the direction of an applied force, transmit rotational motion, or realize a mechanical advantage in either a linear or rotational system of motion. The Southern California punk revival band Pulley was formed upon vocalist Scott Radinskys departure from Ten Foot Pole , brought about by that bands desire for a singer with a full-time focus on music (Radinsky is also a major-league relief pitcher and has played for the Los...
Pulley is a small village on the southern edge of Shrewsbury in Shropshire, England. ...
Image File history File linksMetadata Download high resolution version (2816x2112, 482 KB) Summary Foto of a pulley taken in the city of nl:Kampen by user:GeeKaa Licensing File links The following pages link to this file: Pulley Metadata This file contains additional information, probably added from the digital camera...
Image File history File linksMetadata Download high resolution version (2816x2112, 482 KB) Summary Foto of a pulley taken in the city of nl:Kampen by user:GeeKaa Licensing File links The following pages link to this file: Pulley Metadata This file contains additional information, probably added from the digital camera...
In sailing, a block is a pulley or a number of pulleys enclosed in sheaves so as to be fixed to the end of a line or to a spar or surface. ...
For other uses, see Wheel (disambiguation). ...
A groove is a slot cut into a hard material such as wood, stone, or metal, often to provide a location for another component. ...
The circumference is the distance around a closed curve. ...
Coils of rope used for long-line fishing A rope (IPA: ) is a length of fibers, twisted or braided together to improve strength for pulling and connecting. ...
6 or 15cm outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. ...
v-belt flat belt A Belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. ...
For other uses, see Force (disambiguation). ...
In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. ...
Rope and pulley systems
Rope and pulley systems (the rope may be a light line or a strong cable) are characterized by the use of a single rope transmitting a linear motive force (in tension) to a load through one or more pulleys for the purpose of pulling the load (often against gravity.) They are often included in the list of simple machines. In a system of a single rope and pulleys, the mechanical advantage gained is ideally the number of pulleys in the system (if one pulley is used only to change the direction of the load). The tension in the rope is reduced by the mechanical advantage, while the distance (that is, the length of rope) is increased by the same proportion. Since a slender cable is more easily managed than a fat one (albeit shorter and stronger), pulley systems are often the preferred method of applying mechanical advantage to the pulling force of a winch (as can be found in a lift crane). In physics, a simple machine is any device that only requires the application of a single force to work. ...
Modern self-tailing winch on a sailing boat. ...
A modern crawler type derrick crane with outriggers. ...
In practice, the more pulleys there are, the less efficient a system is. This is due to friction in the system where cable meets pulley and in the rotational mechanism of each pulley. For other uses, see Friction (disambiguation). ...
It is not recorded when or by whom the pulley was first developed. It is believed however that Archimedes developed the first documented block and tackle pulley system, as recorded by Plutarch. Plutarch reported that Archimedes moved an entire warship, laden with men, using compound pulleys and his own strength. For other uses, see Archimedes (disambiguation). ...
This block and tackle on a davit of the Mercator is used to help lower a boat. ...
Mestrius Plutarchus (Greek: ΠλοÏταÏχος; 46 - 127), better known in English as Plutarch, was a Greek historian, biographer, essayist, and Middle Platonist. ...
Types of systems - Fixed A fixed or class 1 pulley has a fixed axle. That is, the axle is "fixed" or anchored in place. A fixed pulley is used to change the direction of the force on a rope (called a belt). A fixed pulley has a mechanical advantage of 1. A mechanical advantage of one means that the force is equal on both sides of the pulley and there is no multiplication of force
- Movable A movable or class 2 pulley has a free axle. That is, the axle is "free" to move in space. A movable pulley is used to multiply forces. A movable pulley has a mechanical advantage of 2. That is, if one end of the rope is anchored, pulling on the other end of the rope will apply a doubled force to the object attached to the pulley.
- Compound A compound pulley is a combination fixed and movable pulley system.
- Block and tackle - A block and tackle is a compound pulley where several pulleys are mounted on each axle, further increasing the mechanical advantage.
Image File history File links Pulley. ...
Image File history File links Pulley. ...
Image File history File linksMetadata Polea-simple-movil2. ...
Image File history File linksMetadata Polea-simple-movil2. ...
An axle is a central shaft for a rotating wheel or gear. ...
v-belt flat belt A Belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. ...
In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. ...
How it works Diagram 1 - A basic equation for a pulley: In equilibrium, the force F on the pulley axle is equal and opposite to the sum of the tensions in each line leaving the pulley, and these tensions are equal. Image File history File links Pulley0. ...
Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ...
| Diagram 2 - A simple pulley system - a single movable pulley lifting a unit weight. The tension in each line is half the unit weight, yielding an advantage of 2. Image File history File links Pulley1. ...
| Diagram 2a - Another simple pulley system similar to diagram 2, but in which the lifting force is redirected downward. Image File history File links Pulley1a. ...
| A practical compound pulley corresponding to diagram 2a. Wikipedia does not have an article with this exact name. ...
| The simplest theory of operation for a pulley system assumes that the pulleys and lines are weightless, and that there is no energy loss due to friction. It is also assumed that the lines do not stretch.
In equilibrium, the total force on the pulley must be zero. This means that the force on the axle of the pulley is shared equally by the two lines looping through the pulley. The situation is schematically illustrated in diagram 1. For the case where the lines are not parallel, the tensions in each line are still equal, but now the vector sum of all forces is zero.
A second basic equation for the pulley follows from the conservation of energy: The product of the weight lifted times the distance it is moved is equal to the product of the lifting force (the tension in the lifting line) times the distance the lifting line is moved. The weight lifted divided by the lifting force is defined as the advantage of the pulley system.
It is important to notice that a system of pulleys does not change the amount of work done. The work is given by the force times the distance moved. The pulley simply allows trading force for distance: you pull with less force, but over a longer distance. In physics, mechanical work is the amount of energy transferred by a force. ...
In diagram 2, a single movable pulley allows a unit weight to be lifted with only half the force needed to lift the weight without assistance. The total force needed is divided between the lifting force (red arrow) and the "ceiling" which is some immovable object (such as the earth). In this simple system, the lifting force is directed in the same direction as the movement of the weight. The advantage of this system is 2. Although the force needed to lift the unit weight is only half of the unit weight, we will need to draw a length of rope that is twice the distance that the weight is lifted, so that the total amount of work done (Force x distance) remains the same.
A second pulley may be added as in diagram 2a, which simply serves to redirect the lifting force downward, it does not change the advantage of the system.
Diagram 3 - A simple compound pulley system - a movable pulley and a fixed pulley lifting a unit weight. The tension in each line is one third the unit weight, yielding an advantage of 3. Image File history File links Pulley2. ...
| Diagram 3a - A simple compound pulley system - a movable pulley and a fixed pulley lifting a unit weight, with an additional pulley redirecting the lifting force downward. The tension in each line is one third the unit weight, yielding an advantage of 3. Image File history File links Pulley2a. ...
| Diagram 4a - A more complicated compound pulley system. The tension in each line is one quarter of the unit weight, yielding an advantage of 4. An additional pulley redirecting the lifting force has been added. Image File history File links Pulley3a. ...
| Figure 4b - A practical block and tackle pulley system corresponding to diagram 4a. Note that the axles of the fixed and movable pulleys have been combined. Wikipedia does not have an article with this exact name. ...
| The addition of a fixed pulley to the single pulley system can yield an increase of advantage. In diagram 3, the addition of a fixed pulley yields a lifting advantage of 3. The tension in each line is ⅓ the unit weight, and the force on the axles of each pulley is ⅔ of a unit weight. As in the case of diagram 2a, another pulley may be added to reverse the direction of the lifting force, but with no increase in advantage. This situation is shown in diagram 3a.
This process can be continued indefinitely for ideal pulleys with each additional pulley yielding a unit increase in advantage. For real pulleys friction among rope and pulleys will increase as more pulleys are added to the point that no advantage is possible. It puts a limit for the number of pulleys we can use in practice. The above pulley systems are known collectively as block and tackle pulley systems. In diagram 4a, a block and tackle system with advantage 4 is shown. A practical implementation in which the connection to the ceiling is combined and the fixed and movable pulleys are encased in single housings is shown in figure 4b. This block and tackle on a davit of the Mercator is used to help lower a boat. ...
Other pulley systems are possible, and some can deliver an increased advantage with fewer pulleys than the block and tackle system. The advantage of the block and tackle system is that each pulley and line is subjected to equal tensions and forces. Efficient design dictates that each line and pulley be capable of handling its load, and no more. Other pulley designs will require different strengths of line and pulleys depending on their position in the system, but a block and tackle system can use the same line size throughout, and can mount the fixed and movable pulleys on a common axle.
Velocity Ratio Pulley systems can comprise of two parts. The Input and Output, Or Driver and Driven, Or Effort and Load.
Output/Driven speeds are called velocity Ratio between wheels in a system is called Velocity Ratio
Velocity Ratio = Distance moved by Effort / Distance moved by Load
Belt and pulley systems A belt and pulley system is characterized by two or more pulleys in common to a belt. This allows for mechanical power, torque, and speed to be transmitted across axes and, if the pulleys are of differing diameters, a mechanical advantage to be realized. Image File history File links Download high-resolution version (738x693, 101 KB) Keilriemen, V-Belt. ...
Image File history File links Download high-resolution version (738x693, 101 KB) Keilriemen, V-Belt. ...
v-belt flat belt A Belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. ...
In physics, power (symbol: P) is the rate at which work is performed or energy is transferred. ...
Torque applied via an adjustable end wrench Relationship between force, torque, and momentum vectors in a rotating system In physics, torque (or often called a moment) can informally be thought of as rotational force or angular force which causes a change in rotational motion. ...
This article does not cite any references or sources. ...
In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. ...
A belt drive is analogous to that of a chain drive, however a belt sheave may be smooth (devoid of discrete interlocking members as would be found on a chain sprocket, spur gear, or timing belt) so that the mechanical advantage is given by the ratio of the pitch diameter of the sheaves only (one is not able to count 'teeth' to determine gear ratio). Roller chain and sprocket Mack AC delivery truck at the Petersen Automotive Museum with chain drive visible Chain drive was a popular power transmission system from the earliest days of the automobile. ...
Belt and pulley systems are systems that can be very efficient, with stated efficiencies up to 98%.
See also Look up Pulley in Wiktionary, the free dictionary. |
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